Installation tool for aerospace fastening system

ABSTRACT

A system, for installation of fastening systems to a structure, includes a fastening system installation specification, which includes dimensional and qualitative requirements for components of the fastening systems; and a tool. The tool includes an outer housing having an interior hollow, a gage surface, and a base surface, the base surface having a contact area that contacts the surface of the structure. An inner plug disposed within the interior hollow translates axially within the interior hollow. The inner plug has a sensing end that contacts a bolt of the fastening system and references the shank section of the bolt. The inner plug has an indicator end dimensioned to accept washers and nuts of the fastening system stacked on the gage surface. The inner plug has an indicator that provides installation information, according to either qualitative or dimensional requirements, about the components of the fastening system being installed using the tool.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional PatentApplication No. 60/533,410, filed on Dec. 29, 2003.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

This invention was made with Government support under contract numberF33657-91-C-0006, awarded by the U.S. Air Force. The Government hascertain rights in this invention.

BACKGROUND OF THE INVENTION

The present invention generally relates to mechanical fastening and,more particularly, to installation of mechanical fastening systems suchas nut, washer, and bolt combinations according to strict installationspecifications.

In the manufacture of commercial and military aircraft, fasteningsystems that fasten various components of the airframe and aircraftstructure may require the fasteners to be installed according to strictinstallation requirements designed to ensure structural efficiency andintegrity. An example of such a fastening system is the familiarcombination of a bolt, nut, and one or more washers, typically used tofasten two components with a clamping action. For certain types ofapplications, the term “pin” may be used synonymously for “bolt”.Setting the fasteners correctly is important.

To accomplish the installation of aerospace fastening systems accordingto the strict requirements designed to maximize structural efficiency ofthe hardware without compromising structural integrity, assembly offastening systems is typically subject to three primary requirements:(1) no “threads in bearing”—meaning that only the unthreaded shanksection of a bolt is allowed to contact the structure being clamped up;(2) no “shanking”—meaning that the nut cannot run so far down thethreads such that the nut enters the thread transition zone of the bolt,where the bolt threads may be incomplete in the vicinity of the shanksection of the bolt; and (3) sufficient “thread protrusion”—meaning thata predetermined amount of thread length must protrude completely throughthe nut to ensure complete nut engagement.

To comply with these, and other, requirements, aerospace fasteningsystems may be required to conform to installation specifications forvarious measurements. For example, a minimum pin protrusion dimensionmay be defined, and specific numerical values may be given for thedimension to exceed, according to the specific fastening system beinginstalled, in order to guarantee compliance with requirement number (1)above.

FIGS. 1A and 1B show a typical fastening system 100 including a bolt 102or pin 102, nut 104, and washer 106 combination. Bolt 102, nut 104, andwasher 106 may be referred to generically as components of fasteningsystem 100. Bolts 102 may be provided in various lengths—called the griplength of the bolt, which is related to the length of shank section 107of bolt 102—depending on the thickness of structure 120 that is to beheld together by the nut-bolt combination and through which the bolt 102may pass. Length may be measured, for example, along longitudinal axis101 of fastening system 100. Bolt 102 may include a threaded sectionhaving a thread length 108. The thread length 108 typically includes athread transition zone 105 in the vicinity of shank section 107 wherethe threads of bolt 102 may be incompletely cut. The end 107 a of shanksection 107 is typically defined by a visible ridge at shank section end107 a between shank section 107 and thread length 108. The visible ridgemay be used as an indication of the transition of shank section 107 intothread transition zone 105 or a boundary between thread transition zone105 and shank section 107.

Different bolts may have a fixed thread length 108 for various griplengths. In other words, a short bolt, such as bolt 102 shown in FIGS.1A and 1B, may have threads cut for a certain length, the thread length108, along the bolt from the end of the bolt, and the thread length 108may be the same for a longer bolt and for a shorter bolt. Because thefasteners may have a fixed thread length 108 for various grip lengths,fasteners are required to conform to installation specificationsregarding the height that the bolt is allowed to protrude, referred toas “protrusion”. More specifically, a minimum pin protrusion 116dimension may be the specified minimum height that bolt 102 may protrudeabove the surface 118 of structure 120, which may be, for example, anaircraft structural component. Minimum pin protrusion 116 may also bereferred to in the art as “minimum pin protrusion to avoid threads inbearing.” Bolt 102 not protruding far enough above the surface 118 toexceed minimum pin protrusion 116 may result in the threaded section ofbolt 102 contacting the structure 120 being clamped up, exemplifying afastening system that does not comply with the “no threads in bearing”requirement number (1) described above. A bolt 102 in which the threadedsection contacts the structure 120 may result in improper fit offastening system 100 to structure 120 as the threaded section of bolt102 is typically smaller in diameter than the shank section 107 of bolt102 for which structure 120 is drilled. Improper fit may lead to damageand possible failure of fastening system 100.

A maximum pin protrusion 110 dimension may be the specified maximumheight that bolt 102 may protrude above the bearing surface 112 of nut104. Maximum pin protrusion 110 may also be measured from the bearingsurface 114 of washer 106, which is in contact with bearing surface 112of nut 104. If the maximum pin protrusion 110 is exceeded, nut 104 couldfully engage the last completely cut thread of the bolt 102 and enterthe thread transition zone 105 before the required compression of thejoint being fastened occurs. Nut 104 entering thread transition zone 105on the bolt 102, or bindingly engaging incomplete threads of transitionzone 105, which may be referred to as “bottoming out” on the threads ofbolt 102, exemplifies a fastening system that does not comply with the“no shanking” requirement number (2) described above. A nut 104 thatbottoms out, or engages the incompletely cut threads of transition zone105, may result in damage to nut 104 and bolt 102, a false torquereading when tightening nut 104, or false clamp-up torque, andinadequate fastening of fastening system 100. Conforming to the maximumpin protrusion 110 specification will preclude, for example, having nutthreads in the thread transition area 105 of the bolt shank and mayensure proper tightening of nut 104 and bolt 102 of fastening system100.

A minimum thread protrusion 122 dimension may be the specified minimumheight that bolt 102 may protrude above nut 104. Conforming to theminimum thread protrusion 122 specification may ensure, for example,that all threads common to the nut 104 and bolt 102 are engaged in orderfor fastening system 100 to function properly. For example, sufficientprotrusion can allow for adequate nut retention due to full nut-to-boltinterference, which can act as an anti-back-off feature. Conversely, athread protrusion that is less than the minimum thread protrusion 122specification may cause fastening system 100 to fail. Bolt 102 notprotruding far enough out of nut 104 to exceed minimum thread protrusion122 exemplifies a fastening system that does not comply with thecomplete nut engagement requirement number (3) described above.

Two unknowns which complicate the washer selection process, i.e.,determining the washer stack for a given fastening system installation,are: (1) the exact dimensions of the actual hardware involved (havingnon-zero tolerances) and (2) the structure thickness through which thebolt protrudes. Since the shoulder—such as the end of shank section 107of bolt 102 at the transition to thread length 108—of the bolt mustalways protrude through the structure to avoid “threads in bearing”, onemight think that one can determine the number of washers in the stack byusing the thread length dimension and nut height. Each of thosedimensions, however, has a tolerance which forces one to account forboth extremes of thread length and nut height. So little thread lengthis available on some fastening systems that variation due tomanufacturing tolerances alone precludes identification of set, oruniversal, washer stack-ups which will work for specific hardware.Therefore, no set washer combination can be defined which will alwaysand simultaneously meet all three installation requirements. Thus, eachinstallation may be regarded as a unique case.

Because each fastening system installation may practically be a uniquecase, ensuring that each fastening system complies with all three of therequirements described above may lead to trial and error methods tocomplete the assembly of the fastening system at each location. Forexample, in the absence of exact measurements of the particularfastening system being installed, a mechanic must sometimes use a trialand error process all the way through torque-up of the fastening systemto determine if the selected washer stack-up meets requirements. Withtoo small a stack of washers, the nut will engage the shoulder of thebolt below the threads (shanking), and with too large a stack, the nutwill not be fully engaged with the bolt (insufficient thread protrusionthrough the top of the nut). Thus, a tool is needed that can helpdetermine how a successful fastening system installation can be madewithout a trial and error process and prior to torque-up of thefastening system.

Currently, installation specifications monitor a minimum pin protrusiondimension—such as minimum pin protrusion 116 shown in FIG. 1A—to be surethat enough bolt is protruding through structure—such as structure120—so that even with tolerances, the fastening system cannot have“threads in bearing”. A maximum pin protrusion dimension—such as maximumpin protrusion 110—is monitored to be sure that there is not so muchthread length extending above the washers that the nut could haveengaged incomplete threads near the shoulder below the threads(shanking). A minimum thread protrusion dimension—such as minimum threadprotrusion 122—is monitored to be sure enough thread protrudes throughthe top of the nut to give confidence that the nut is fully engaged infully formed threads and will not back off. For each type of fasteningsystem, numerical specifications are given for each dimension, so thatwhen the fastening system is within the numerical specification it issaid to meet, or conform to, a dimensional requirement—such as minimumpin protrusion—for that type of fastening system. The values of thenumerical specifications, i.e., the dimensional requirements, are setwith regard to the tolerances so that when the dimensional requirementsfor minimum pin protrusion, maximum pin protrusion, and minimum threadprotrusion are met, the fastening system will meet the qualitativerequirements of having no “threads in bearing”, no shanking, andcomplete nut engagement, respectively.

As can be seen in FIG. 1A, the dimensions (minimum pin protrusion,maximum pin protrusion, and minimum thread protrusion) overlap and soare not independent of one another. In order to guarantee that afastening system will meet the qualitative requirements (e.g. no“threads in bearing”), the numerical specifications for the dimensionalrequirements (e.g. minimum pin protrusion) must cover every possiblecase of tolerance variation, including the worst on worst tolerancecases—for example, a tallest nut within tolerances combined with a bolthaving a shortest thread length within tolerances. Thus, it can bedifficult to simultaneously meet all three dimensional requirements,particularly, for example, where a fastening system has limited threadlength. Thread length must be sufficient for up to one wasted washer(where an additional washer was just barely needed), the tallest nutwithin tolerances, and the required thread protrusion. The dimensionalrequirement—for thread length, for example—is restrictive in the sensethat a fastening system installation can be made that meets all thequalitative requirements without meeting all the dimensionalrequirements. Thus, the dimensional requirements are more restrictivethan the qualitative requirements because of the need for thedimensional requirements to guarantee that the qualitative requirementsare met over all tolerance cases.

Prior art measurement tools typically take some sort of numericalmeasurement of one of the installed fastening system dimensions—such asa pin protrusion dimension—and so are adaptable almost exclusivelytoward working in conjunction with dimensional requirements rather thanqualitative requirements. If the fastening system 100 fails to meet anyof the dimensional requirements, it is deemed not to conform to theinstallation specification, i.e., fastening system 100 does not meet thedimensional requirements. In such a case, the fastening systeminstallation is assumed not to meet the qualitative requirements, andthe installation is rejected. It is still possible in such a case,however, due to combinations of variation of the components withintolerances, as described above, for the installation to actually meetthe qualitative requirements even though the dimensional requirementsare not met. Thus, the prior art gages are generally not helpful in theefficient selection, without trial and error, of proper bolt, washer,and nut combinations for each unique case that arises out of eachdistinct location of a fastening system installation on a structure.

As can be seen, there is a need for a tool for installation of fasteningsystems—such as nut and bolt fastenings used on aircraft—according tostrict installation specifications that are designed to meet bothdimensional and qualitative requirements. There is also a need for atool for installation of fastening systems that facilitates efficientselection, in a predictive manner avoiding trial and error, of a properbolt, washer, and nut combination for each unique case of fasteningsystem installation at distinct locations on a structure. Moreover,there is a need for an installation tool that provides a combination ofmeasurements at one time, accounting for the interactions of tolerancesbetween different fastening system dimensions whose specifications allneed to be met simultaneously. Furthermore, there is a need for afastening system installation system including an installation tool anda new type of installation specification that allows fastening systeminstallations to be made directly according to qualitative requirementsand that is less restrictive than prior art installation specificationslimited to dimensional requirements.

SUMMARY OF THE INVENTION

In one aspect of the present invention, a fastening system installationtool, for installation of a fastening system to a structure, includes anouter housing having an interior hollow, a gage surface, and a basesurface. The base surface has a contact area that contacts the surfaceof the structure. An inner plug is disposed within the interior hollowand translates axially within the interior hollow. The inner plug has asensing end that contacts the fastening system and an indicator enddimensioned to accept washers and nuts of the fastening system stackedon the gage surface. The inner plug has an indicator at the indicatorend that provides installation information according to a fasteningsystem installation specification about washers and nuts of thefastening system stacked on the gage surface.

In another aspect of the present invention, a fastening systeminstallation tool, for installation of a fastening system to astructure, includes an outer housing having an interior hollow, a gagesurface, and a base surface. The base surface has a contact area thatcontacts the surface of the structure. An inner plug is disposed withinthe interior hollow and translates axially within the interior hollow.The inner plug has a sensing end that contacts the fastening system andan indicator end dimensioned to accept washers and nuts of the fasteningsystem stacked on the gage surface. The inner plug has an indicator onthe indicator end that indicates whether a fastening system componentselection allows conformance to a qualitative requirement of a fasteningsystem installation specification.

In still another aspect of the present invention, a system, forinstallation of a fastening system to a structure, includes a fasteningsystem installation specification, which includes dimensionalrequirements for components of a fastening system; and a tool. The toolincludes an outer housing having an interior hollow, a gage surface, anda base surface, the base surface having a contact area that contacts thesurface of the structure. An inner plug is disposed within the interiorhollow and translates axially within the interior hollow. The inner plughas a sensing end that contacts a bolt of the fastening system andreferences the shank section of a bolt of the fastening system. Theinner plug has an indicator end dimensioned to accept washers and nutsof the fastening system stacked on the gage surface, and the inner plughas an indicator on the indicator end that provides installationinformation according to the fastening system installation specificationabout the components of the fastening system being installed using thetool.

In yet another aspect of the present invention, an installation systemis disclosed for installing aerospace fastening systems to a structure.The installation system includes an installation guide, in accordancewith qualitative requirements for components of a fastening system, anda tool. The tool includes an outer housing having an interior hollow, agage surface, and a base surface, the base surface having a flat contactarea that contacts the surface of the structure. The tool includes aninner plug disposed within the interior hollow and translates axiallywithin the interior hollow. The inner plug has a sensing end with anaxial bore that contacts the fastening system, and the sensing endreferences the shank section of a bolt of the fastening system. Theinner plug also has an indicator end. A transducer is connected betweenthe outer housing and the inner plug and measures a relativedisplacement between the inner plug and the outer housing. Electronicinstrumentation is connected to the transducer and provides and displaysinstallation information according to the installation guide aboutwhether the bolt, washer, and nut components of the fastening systembeing installed using the tool will conform to a fastening systeminstallation specification.

In a further aspect of the present invention, a method is disclosed forinstalling aerospace fastening systems to a structure. The methodincludes the steps of: seating a base of an outer housing of a tool to asurface of the structure; referencing a shank section of a bolt of thefastening system with an inner plug of the tool; reading athreads-in-bearing indicator of the inner plug in conjunction with agage surface of the outer housing; replacing the bolt when thethreads-in-bearing indicator is not above the gage surface; andinstalling the bolt when the threads-in-bearing indicator is above thegage surface.

In a still further aspect of the present invention, a method forinstalling an aerospace fastening system to a structure includes thesteps of: seating a base of an outer housing of a tool to a surface ofthe structure; referencing a shank section of a bolt of the fasteningsystem with an inner plug of the tool; and reading an indicator of thetool to determine a prescribed washer stack for the fastening system.

In yet a further aspect of the present invention, a method forinstalling aerospace fastening systems to a structure includes the stepsof: inserting a bolt of the fastening system in a hole of the structure;checking for a protrusion of a shank section of the bolt above a surfaceof the structure; replacing the bolt when the shank section does notprotrude above the surface of the structure; seating a base of an outerhousing of a tool to a surface of the structure; referencing a shanksection of a bolt of the fastening system with an inner plug of thetool; stacking a first washer on a gage surface of the tool to form astack; reading a shanking indicator of the inner plug in conjunctionwith the top of the stack; and adding an additional washer to the stackwhen the top of the stack is below the shanking indicator.

These and other features, aspects and advantages of the presentinvention will become better understood with reference to the followingdrawings, description and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a cross-sectional diagram of a prior art nut and boltfastening system, illustrating various measurements;

FIG. 1B is an isometric view of the prior art fastening system shown inFIG. 1A;

FIGS. 2A and 2B are perspective illustrations of a fastening systeminstallation tool, according to one embodiment of the present invention,showing placement of the tool relative to a structure and fasteningsystem;

FIG. 2C is a side, cross-sectional, diagrammatical view of a fasteningsystem installation tool, according to one embodiment of the presentinvention, showing placement of the tool relative to a structure andfastening system;

FIG. 3 is a side, cross-sectional diagram of a fastening systeminstallation tool, according to another embodiment of the presentinvention;

FIGS. 4A and 4B are side, cross-sectional diagrams of a fastening systeminstallation tool, showing how the same tool can be used to perform twodifferent measurements, according to still another embodiment of thepresent invention;

FIG. 5 is a side, cross-sectional diagram of a fastening systeminstallation tool, according to yet another embodiment of the presentinvention;

FIG. 6A is a side, cross-sectional diagram of a fastening systeminstallation tool incorporating an automated readout, according to yetanother embodiment of the present invention; and

FIG. 6B is a table showing an exemplary installation guide, inaccordance with an embodiment of the present invention, and illustratesan exemplary correspondence of readouts of a fastening systeminstallation tool with exemplary washer stack prescriptions.

DETAILED DESCRIPTION OF THE INVENTION

The following detailed description is of the best currently contemplatedmodes of carrying out the invention. The description is not to be takenin a limiting sense, but is made merely for the purpose of illustratingthe general principles of the invention, since the scope of theinvention is best defined by the appended claims.

Broadly, an embodiment of the present invention provides a tool forinstallation of fastening systems, such as nut and bolt fastenings usedon aircraft. The tool, in one embodiment, may not only facilitatemeasurement for various installation specifications—such as measurementof pin protrusion—required for installation of aerospace fasteningsystems according to strict dimensional requirements, but may alsofacilitate proper selection of fastening system components to ensureadherence to qualitative requirements designed to maximize structuralefficiency of the hardware without compromising structural integrity.The tool of one embodiment may be used with a fastening machine used forinstalling fastening systems. For example, the tool may be used to checkfor conformance to specifications of fastening systems being installedby machine.

A tool according to one embodiment may also facilitate efficientselection—avoiding trial and error installations, for example—of properbolt, washer, and nut combinations for assembly of fastening systems foreach unique case of fastening system installations at distinct locationson a structure so that the assembled fastening systems conform toqualitative requirements, for example, regarding (1) no “threads inbearing”; (2) no “shanking”; and (3) complete nut engagement. A basicpremise of the various embodiments, illustrated herein by example, isthat a tool according to an embodiment enables the mechanic to query atleast one dimension of the fastening system hardware to determine how asuccessful installation can be made without a trial and error process.The tools according to the embodiments illustrated may measure at leastone dimension on an actual bolt, sometimes looking at the thread lengthonly (a dimension which is actually independent of the structure) andsometimes looking at the extent to which the bolt protrudes through thestructure. Without this information the mechanic must sometimes maketrial and error installations to determine what washer stack-up isneeded. Too few washers in a stack, and the nut will engage the shoulderof the bolt below the threads (shanking). Too many washers in the stack,and there will be insufficient thread protrusion through the top of thenut. Use of a tool which queries the actual bolt to be installed removesuncertainties due to the dimensional variation of the specific boltwithin tolerances and, if the tool also queries other hardware such asthe washers or nut, or both, the dimensional variations associated withtolerances for those components no longer come into play either. Use ofa tool on the actual bolt as trial fit in structure removes thestructure thickness variable and further delineates the true washerstack requirement. The degree to which more than one hardware orstructure dimension needs to be queried depends upon the hardwaretolerances and installation requirements involved with the particularfastening system. Depending on the tolerances involved, the tool may beable to result in an installation which still meets all of the existingdimensional requirements. However, the dimensional requirements are morehighly restrictive than the qualitative requirements because thedimensional requirements guarantee meeting requirements over alltolerance cases of the hardware. Therefore, use of a tool whicheliminates some of the unknowns stemming from tolerances via gauging thehardware, may guarantee that the qualitative requirements have been meteven though the installation may not result in values meeting the priorart dimensional requirements. The desire to meet the dimensionalrequirements versus the qualitative requirements may influence whichtype of tool may be used for installation of fastening systems.

In one embodiment, an installation tool may provide a combination ofmeasurements at one time, accounting for the interactions of tolerancesbetween different fastening system dimensions whose specifications allneed to met simultaneously. One embodiment may provide a fasteningsystem installation system including an installation tool and a new typeof method of installation that allows fastening system installations tobe made directly according to qualitative requirements. The new type ofmethod of installation according to qualitative requirements may be lessrestrictive than prior art methods of installation according tospecifications that are limited to dimensional requirements.Accordingly, fastening system specifications, according to an embodimentof the present invention, may be designed differently from prior artfastening system specifications, so that accounting for tolerances forsome dimensions may be eliminated via measurement or gauging. By way ofcontrast, prior art specifications generally must assume that alltolerances are expressed as dependent on quantities that are themselvessubject to tolerances rather than on known quantities. Thus, in oneembodiment, a new type of method for fastening system installationaccording to the less restrictive qualitative requirements may allow,for example, for improved labor efficiency in installing fasteningsystems as well as relaxation of tolerances on some fastening systemhardware.

Three examples can be given of general approaches for exploiting theadvantages gained by the new installation tool and methods ofinstallation. First, the new tools and methods may be used to enablesuccessful installations with more thread length efficiency than priorart installations, thus allowing a reduction in thread length and weightsavings. While weight savings are important for aircraft, a small weightsavings would result if thread lengths were reduced, and so thisapproach may be less likely to be used. Second, the new tools andmethods may be used to enable a relaxation in fastening system hardwaretolerances, thus providing a cost savings. Due to broad industry use ofsome fastening systems, however, this approach also may be less likelyto be used. Third, the new tools and methods may be used to continueusing the fastening system hardware in use while increasing shopefficiency by reducing trial and error installations and rejections.This approach appears to be the most likely to provide a readily gainedadvantage.

Also in contrast to the prior art, the tool according to one embodimentmay provide measurement indications in a graphical or physical formatduring installation of fastening systems so that the tool facilitatesefficient selection of proper bolt, washer, and nut combinations for theunique case of each location of a fastening system installation on astructure—such as an aircraft part or aerospace product. A graphicalformat indication may be given, for example, by a display providingresults such as those shown in FIG. 6B. A physical format indication maybe given, for example, by stacking washers on a tool with shoulders sothat if the washers fit evenly against or above a particular shoulder,it is known that a proper installation of the fastening system willresult.

Further in contrast to the prior art, the tool of one embodiment mayincorporate a plunger or an inner plug, or both, that have a novelstructure that is specifically formed in accordance with fasteningsystem requirements, in order to provide direct assistance in theselection of proper bolt, washer, and nut combinations. A part of thenovel structure, for example, may include the formation of shoulders atspecific heights and locations on the inner plug (or plunger or both) orthe formation of color bands at specific heights and locations on theinner plug (or plunger or both), corresponding to fastening systeminstallation specifications in such a way that, for example, the actualwashers to be used can be stacked on the tool to determine whether thoseparticular washers will conform to installation specificationrequirements when assembled with the fastening system being measured bythe tool. Another part of the novel structure, for example, may includea plunger with a sliding fit within an interior hollow of an inner plugto measure, for example, a particular pin protrusion according to aspecification. Different inner plugs (or plungers or both) may beprovided for different size fastening systems so that, for example, theinner plug may be threaded or otherwise fitted to give a preciseshanking measurement for a particular size fastening system.

In one embodiment, a fastening system installation and measurement toolmay be interfaced to an electronic system through the use of atransducer connected to the tool. Software may be created and used toprovide specifically needed user information or a simple digitalmeasurement readout.

Referring now to the figures, in which like items are referenced withthe same numeral throughout, and referring, in particular, to FIGS. 2A,2B, and 2C, an aerospace fastening system installation tool 200 isillustrated in accordance with one embodiment. Tool 200 may include anouter housing 202, which may also be referred to as an outer sleeve 202.Outer housing 202 may have an interior hollow 204 which may be an axialbore that extends parallel to the direction of a longitudinal axis 206of tool 200. Outer housing 202 may include a base surface 208, which maycontact surface 118 of structure 120 and which may firmly seat tool 200on surface 118. Base surface 208 may be flat. Base surface 208, forexample, may have an annular shape that may surround an opening largerthan a diameter of a bolt 102 of the fastening system 100 so that thecontact area of base surface 208 with surface 118, or “footprint” ofouter housing 202, may allow passage of the threaded section and shanksection of a bolt 102 of a fastening system 100 into interior hollow 204of outer housing 202. The contact area of base surface 208, or“footprint” of outer housing 202, also, for example, may resemble thefootprint of a washer 106 of fastening system 100. Outer housing 202 mayinclude a gage surface 210. Gage surface 210 may be flat within anaccuracy sufficient to provide consistent or precise readings of tool200 in accordance with a fastening system installation specification, asfurther described below. Gage surface 210 may be perpendicular tolongitudinal axis 206. Gage surface 210 may also be formed at anoblique, or non-perpendicular angle to longitudinal axis 206 so that,for example, gage surface 210 could be a conical surface if desired.Outer housing 202 may be made, for example, of nylon.

Tool 200 may include an inner plug 212, which may also be referred to asan inner sleeve 212. Inner plug 212 may be disposed within interiorhollow 204 of outer housing 202 so that inner plug 212 may translateaxially, i.e., in a direction parallel to longitudinal axis 206, withininterior hollow 204, guided by interior hollow 204. An example of therelative motion, which may be a telescoping or sliding motion, of outerhousing 202 and inner plug 212 during operation of tool 200 isillustrated by FIGS. 2A and 2B. A more detailed description of theoperation of tool 200 is provided further below. Thus, when outerhousing 202 of tool 200 is placed over a fastening system 100, asindicated by arrow 201, shown in FIG. 2A, inner plug 212 may bedisplaced axially with respect to outer housing 202 by bolt 102 offastening system 100, resulting in axial displacement 213, shown in FIG.2B, of threads-in-bearing shoulder 224 relative to gage surface 210,which are shown, for example, in FIG. 2A as being initially flush witheach other. Inner plug 212 may be made, for example, of hard tool steel,and may have a free sliding fit inside of outer housing 202 or may havean interference fit or frictional fit inside of housing 202, dependingon a particular application for which the tool 200 may be intended. Forexample, in applications where tool 200 may be used while remaining inplace over a fastening system 100, a free sliding fit may be preferable.Also, for example, in applications where tool 200 may need to be removedfrom over a fastening system 100 during use, a frictional fit thattemporarily preserves the axial displacement 213 of inner plug 212relative to outer housing 202 may be preferable.

Inner plug 212 may have a sensing end 214 that may contact bolt 102.Inner plug 212 may have an axial bore 216, i.e., a bore which extendsparallel to the direction of longitudinal axis 206. Axial bore 216 mayextend through the sensing end 214 of inner plug 212 so that bolt 102may enter interior hollow 204.

As seen in FIG. 2C, axial bore 216 may have a diameter 218 that isgreater than the thread diameter of a bolt 102 of the fastening system100 but less than the shank diameter 119 (shown in FIG. 1A) of shanksection 107 of bolt 102 of the fastening system 100. For example,diameter 218 may be approximately 0.001 inch greater than the threaddiameter of bolt 102. Thus, when tool 200 is placed over fasteningsystem 100, sensing end 214 may slide freely over the thread length 108of bolt 102 until sensing end 214 reaches the shank section 107 of bolt102 and stops, in which situation inner plug 212, or sensing end 214 ofinner plug 212, is said to “reference” the shank section 107 of bolt102.

Alternatively, for example, axial bore 216 may be threaded to match thethreads of bolt 102 so that inner plug 212 may be screwed onto bolt 102until sensing end 214 reaches the shank section 107 of bolt 102 andstops, thus referencing the shank section 107 of bolt 102. Threading ofaxial bore 216 may add confidence during operation of tool 200 thatmating of fastening system 100 to structure 120 is reasonably “firm” butmay necessitate, for example, either splining of inner and outer sleeves212 and 202 to transmit torque from outer sleeve 212 to inner sleeve 202or sequential placement of inner and outer sleeves 212 and 202 duringoperation of tool 200. Also, threading of axial bore 216 may necessitateeither that the measurement made by the tool 200 be read with tool 200left in place or that tool 200 resist losing the measurement while beingspun off the bolt, for example, by use of a mechanically “stiff”frictional fit between inner plug 212 and outer housing 202 of tool 200or electronic retention of the measurement using a transducer andelectronic instrumentation as described below with reference to FIG. 6A.

Inner plug 212 may also be configured as shown in FIG. 4A, for example,without an axial bore 216, so that sensing end 214 stops upon contact ofinner plug 212 with an end 124 of bolt 102 of a fastening system 100, inwhich situation inner plug 212, or sensing end 214 of inner plug 212, issaid to “reference” the end 124 of bolt 102.

Continuing with FIGS. 2A, 2B, and 2C, inner plug 212 may have anindicator end 220. Indicator end 220 may be dimensioned to acceptwashers 106 and nuts 104 of the fastening system 100 stacked on gagesurface 210, as shown in FIG. 2C. For example, indicator end 220 mayhave a diameter 222 that is approximately 0.020 inch less than thethread diameter of bolt 102 for allowing a nut 104 to be easily stackedon inner plug 212. FIGS. 2A, 2B, and 2C show an example of a tool thatgives measurement indications in a physical format, as described above,using shoulders as indicators that are readable in conjunction with gagesurface 210, for example, by noting whether the shoulder is below, evenwith, or above gage surface 210. Similarly, the shoulder indicators maybe readable in conjunction with fastening system components—such aswashers and nuts—stacked on gage surface 210, for example, by notingwhether the shoulder is below, even with, or above a top surface of thecomponent. The shoulders may be used as indicators to provideinstallation information about components of the fastening system beinginstalled using the tool—such as washers 106 and nut 104 of thefastening system stacked on gage surface 210 as shown in FIG. 2C. Theindicators may provide installation information—such as whether theinstallation conforms to qualitative and dimensionalrequirements—according to a strict fastening system installationspecification.

For example, inner plug 212 may have an indicator at indicator end 220in the form of threads-in-bearing shoulder 224. If threads-in-bearingshoulder 224 is translated up from its initial flush condition withrespect to gage surface 210, i.e., if axial displacement 213 is apositive finite amount, it may be known that fastening system 100 shownin FIG. 2C conforms to the qualitative requirement of “no threads inbearing”. Shanking shoulder 225 may indicate whether fastening system100 will conform to the qualitative requirement of “no shanking” uponinstallation of washers 106. For example, upon installation of washer106 a, fastening system 100 will not conform to “no shanking” becausethe top surface 109 of washer 106 a is below shanking shoulder 225; asshown in FIG. 2C. Upon installation of washer 106 b, however, fasteningsystem 100 will conform to “no shanking” because the top surface 111 ofwasher 106 b may be either above or even with shanking shoulder 225, asshown in FIG. 2C.

Inner plug 212 may have another indicator in the form of short-threadbolt protrusion shoulder 226. Inner plug 212 also may have anotherindicator in the form of long-thread bolt protrusion shoulder 228. Thetwo thread bolt protrusion shoulders 226 and 228 may be provided tocover two different cases of long-thread and short-thread bolts 102,which may be manufactured with purposefully designed short or longthread length 108 sections. (The “long” and “short” in this instancerefer to the type of bolt being used, and not to tolerances of threadlength sections.)

For example, for a bolt 102 having a short thread length 108, i.e., ashort-thread bolt, short-thread bolt protrusion shoulder 226 mayindicate whether fastening system 100 will conform to the qualitativerequirement of complete nut engagement upon installation of nut 104. Forexample, upon installation of appropriate washer stack 106 and nut 104,fastening system 100 will conform to “complete nut engagement” becausethe top surface 113 of nut 104 is below short-thread bolt protrusionshoulder 226, as shown in FIG. 2C. On the other hand, if top surface 113of nut 104 is above short-thread bolt protrusion shoulder 226, thenthere is insufficient thread protrusion for complete nut engagement forthe particular nut 104, washer stack 106, and short-thread bolt 102being installed, and one or the other (nut 104 or bolt 102) should bereplaced or, alternatively, a long-thread bolt 102 may be selected forinstallation. For a bolt 102 having a long thread length 108, i.e., along-thread bolt, long-thread bolt protrusion shoulder 228 may indicatein a similar fashion to that just described whether fastening system 100will conform to the qualitative requirement of complete nut engagementupon installation of nut 104 to a long-thread bolt 102. Threadprotrusion shoulders 226 and 228 also may be similarly used to verifythe dimensional requirement of minimum thread protrusion in addition tothe qualitative requirement of complete nut engagement.

The precise locations of and distances between the indicators—such asshoulders 224, 225, 226, and 228—may be chosen according to a fasteningsystem installation specification for the particular fastening systemsthat the tool is to used with. For example, the distance betweenthreads-in-bearing shoulder 224 and short-thread bolt protrusionshoulder 226 may correlate to the specifications given for bolt 102,taking into account the worst case tolerance combinations, as describedabove. Also, for example, the positions and distances betweenthreads-in-bearing shoulder 224, shanking shoulder 225, and short-threadbolt protrusion shoulder 226 may correlate to the dimensionalspecifications, such as maximum pin protrusion 110, minimum pinprotrusion 116, and minimum thread protrusion 122. It should be notedthat the heights of surfaces 226 and 228 relative to surfaces 224 mustbe configured to account for the required thread protrusion. Since tool200 does not query the bolt end, e.g. inner plug 212 does not referencebolt end 124 in FIG. 2C, tool 200 should take thread length toleranceinto account, and the heights of surfaces 226 and 228 relative tosurface 224 should correspond to the “minimum thread length within bolttolerance” less the required thread protrusion. Thus, tool 200 may beused not only to provide installation according to qualitativerequirements, as described above, but may also be used to provideinstallation according to dimensional requirements in the moreconventional manner. Use of tool 200 to provide direct informationaccording to qualitative requirements, however, has several advantagesover the prior art, as described above.

Using a tool—such as tool 200, a method of installing aerospacefastening systems—such as a bolt 102, washer 106, and nut 104combination—may include the following steps. Insert bolt 102 fully instructure 120 hole. If the tool—such as tool 200—does not have athreads-in-bearing indicator—such as threads-in-bearing shoulder224—then check for the existence of shank 107 protruding above structuresurface 118. If shank 107 is not above structure surface 118, replacebolt 102 due to “threads in bearing”. In other words, bolt 102 does notmeet the qualitative requirement of no “threads in bearing” and so abolt 102 with a longer shank section 107 should be installed. The abovesteps are repeated until shank 107 protrudes above structure surface118. With shank 107 above structure surface 118, place the tool 200 withan outer housing 202 having a base surface 208 on a structuresurface—such as surface 118 of structure 120—seating base surface 208 ofouter housing 202 where the washers 106 will eventually sit. As theouter housing 202 is seated over bolt 102, the inner plug 212 willtelescope up as commanded by contact with the bolt 102. To fully seatthe inner plug 212, thread or slide inner plug 212 onto bolt 102 untilinner plug 212 shanks bolt 102 or cannot go on more, i.e., until sensingend 214 of inner plug 212 references the shank section 107 of bolt 102.Add actual washers 106 stacked on gage surface 210 and continue with themethod at this point, as described below.

If the tool—such as tool 200—does have a threads-in-bearingindicator—such as threads-in-bearing shoulder 224—then place the tool200 with an outer housing 202 having a base surface 208 on a structuresurface—such as surface 118 of structure 120—seating base surface 208 ofouter housing 202 where the washers 106 will eventually sit. As theouter housing 202 is seated over bolt 102, the inner plug 212 willtelescope up as commanded by contact with the bolt 102. To fully seatthe inner plug 212, thread or slide inner plug 212 onto bolt 102 untilinner plug 212 shanks bolt 102 or cannot go on more, i.e., until sensingend 214 of inner plug 212 references the shank section 107 of bolt 102.Read a threads-in-bearing indicator—such as threads-in-bearing shoulder224 of inner plug 212—in conjunction with gage surface 210 of outerhousing 202. If threads-in-bearing shoulder 224 is not above outerhousing gage surface 210, the mechanic may remove the tool 200 andvisually double check the bolt 102 to make sure that the end 107 a ofthe shank section 107 is either flush with or above surface 118 so thatthere are no threads in bearing, or may replace bolt 102 due to “threadsin bearing”. In other words, bolt 102 does not meet the qualitativerequirement of no “threads in bearing” and so a bolt 102 with a longershank section 107 should be installed. The above steps are repeateduntil threads-in-bearing shoulder 224 is above outer housing gagesurface 210. With threads-in-bearing shoulder 224 above outer housinggage surface 210, add actual washers 106 stacked on gage surface 210, asin the case of a tool with no threads-in-bearing indicator describedabove, and continue the method by reading the shanking indicator—such asshanking shoulder 225 of inner plug 212—in conjunction with the top ofthe stack until washers 106 stack even with or above, i.e. not below,shanking shoulder 225 to validate the qualitative requirement of no“shanking”.

Add actual nut 104 to the stack on gage surface 210 and verify boltprotrusion meeting the dimensional requirement of minimum threadprotrusion or the qualitative requirement of complete nut engagement byreading a thread bolt protrusion indicator—such as short-thread boltprotrusion shoulder 226 or long-thread bolt protrusion shoulder 228—ofinner plug 212 in conjunction with nut 104. Both long and short boltthread length indicators may be included in the gage indicators of innerplug 212. For example, in order to meet the complete nut engagementqualitative requirement, the top surface 113 of nut 104 should be belowshort-thread bolt protrusion shoulder 226 for a short-thread bolt 102,and the top surface 113 of nut 104 should be below long-thread boltprotrusion shoulder 228 for a long-thread bolt 102. If the top surface113 of a nut 104 is above the appropriate indicator, the nut or boltshould be replaced due to not meeting the complete nut engagementqualitative requirement and a nut or bolt meeting the complete nutengagement qualitative requirement may be installed. A minimum threadprotrusion dimensional requirement may be similarly verified.

Referring now to FIG. 3, a fastening system installation tool 250 isillustrated in accordance with another embodiment. Fastening systeminstallation tool 250 may be similar in form and function to fasteningsystem installation tool 200 and may include an outer housing or sleeve202, which may be made, for example, from nylon, with base surface 208,an interior hollow 204 oriented along longitudinal axis 206, and a gagesurface 210, as described above. Tool 250 may also include an inner plugor sleeve 212, which may be made, for example, from hard tool steel,with a sensing end 214, an axial bore 216 having diameter 218, and anindicator end 220 with maximum diameter 222, as described above. Innersleeve 212 may be made to have an interference fit with outer sleeve202, also as described above. Indicator end 220 may include indicatorssuch as threads-in-bearing color band 252, shanking color band 254,short-thread bolt minimum thread protrusion color band 256, andlong-thread bolt minimum thread protrusion color band 258. Color bands252, 254, 256, and 258 may have positions and distances between colorbands(e.g. color band thicknesses) to correlate to a dimensionalrequirement of the fastening system installation specification, asdescribed above in the case of shoulders 224, 225, 226, and 228,respectively. For example, the edge of a color band (or boundary betweentwo color bands) of tool 250 may have the same position, or distancefrom sensing end 214, as a shoulder of tool 200. Color bands 252, 254,256, and 258 may be used, for example, in a manner similar to that ofshoulders 224, 225, 226, and 228 as described above for the installationof fastening systems such as fastening system 100, including thestacking of fastening system components over indicator end 220 on gagesurface 210. In addition, any color band—such as shanking color band254—may be subdivided further, for example, using index markings oradditional color bands, to increase the flexibility or specialized useof the installation tool—such as tool 250. For example, supplyingadditional color bands or index markings in the region of shanking colorband 254 may enable selection of appropriate washers in accordance withavailable washer thicknesses, using, for example, the method describedbelow in connection with exemplary installation guide 290 shown in FIG.6B.

More specifically, methods of using tool 250 for the installation offastening systems—such as fastening system 100—according to strictdimensional and qualitative requirements may include a mechanicinserting a bolt—such as bolt 102—through a joint in a structure—such asstructure 120—that is to be fastened and placing installation tool 250over the thread end of the bolt 102. The tool 250 may be used to measurethe location of the bolt shoulder relative to the surface 118 ofstructure 120, i.e., sensing end 214 reaches the shank section 107 ofbolt 102 and stops, thus referencing the shank section 107 of bolt 102.Due to an interference fit between outer sleeve 202 and inner sleeve212, inner sleeve 212 may maintain its position relative to outer sleeve202 after the mechanic has removed tool 250 from the threads of bolt102.

Next, threads-in-bearing color band 252 may be read in conjunction withgage surface 210 to determine compliance with a no threads-in-bearingqualitative requirement. The mechanic may check to see if thethreads-in-bearing color band 252 is visible above gage surface 210. Ifthreads-in-bearing color band 252 is visible above gage surface 210, theinstallation may meet the no threads in bearing qualitative requirement;otherwise bolt 102 should be replaced, as described above.

Shanking color band 254 may then be read in conjunction withwashers—such as washer 106—stacked on gage surface 210 (as shown in FIG.2C). The mechanic may use the minimum number of washers required tocompletely cover the shanking color band 254 to ensure that theinstallation meets the no shanking qualitative requirement, oralternatively a maximum pin protrusion 110 dimensional requirement.Stacking the actual washers to be used in the particular installationbeing performed and measured may account for washer thicknesstolerances, i.e. removes uncertainties due to the dimensional variationof the specific washers within tolerances.

Short-thread bolt minimum thread protrusion color band 256 may be readin conjunction with a nut—such as nut 104—stacked on washers 106 on gagesurface 210 (as shown in FIG. 2C) to ensure that a dimensionalrequirement of minimum thread protrusion, or a qualitative requirementof complete nut engagement is met when a short-thread bolt 102 isinstalled. The mechanic may place the nut 104 to be used in theinstallation assembly on top of the stack of washers 106. If any ofshort-thread bolt minimum thread protrusion color band 256 shows abovethe top of the nut 104, the installation will meet the minimum threadprotrusion or complete nut engagement requirement. Measuring the actualnut and washers to be used in the particular installation beingassembled may account for both the tolerances applied to the total nutheight and the washer thickness.

Similarly, long-thread bolt minimum thread protrusion color band 258 maybe used as described above when a long-thread bolt 102 is installed.

Referring now to FIGS. 4A and 4B, a fastening system installation tool260 is illustrated in accordance with another embodiment. Fasteningsystem installation tool 260 may be similar in form and function tofastening system installation tools 200 and 250 and may include an outerhousing or sleeve 202, with a gage surface 210 and a base surface 208,which may be seated on a structure—such as surface 118 of structure 120as shown in FIG. 4A—or on a stack of washers 106 as shown in FIG. 4B.

Tool 260 may also include an inner plug 212, with a sensing end 214,which may reference an end of a bolt—such as end 124 of bolt 102. Innersleeve 212 may be made to have an interference fit or a sliding fit withouter sleeve 202, as described above. Inner plug 212 may have anindicator end 220. Indicator end 220 may include indicators such asindex markings 262. Index markings 262 may have positions and distancesbetween index marks that correlate to dimensional requirements of thefastening system installation specification, as described above in thecase of shoulders 224, 225, 226, and 228. Index markings 262 also, forexample, may be numerically labeled and conform to a standard ofmeasurement such as inches or millimeters.

When used as shown in FIG. 4A, installation tool 260 may provide aminimum pin protrusion measurement 264, corresponding to a minimum pinprotrusion 116 dimension of a fastening system installationspecification and, thus, may be used to verify a minimum pin protrusiondimensional requirement. When used as shown in FIG. 4B, with basesurface 208 placed on top of a stack of washers 106, installation tool260 may provide a maximum pin protrusion measurement 266, correspondingto a maximum pin protrusion 110 dimension of a fastening systeminstallation specification and, thus, may be used to verify a maximumpin protrusion dimensional requirement. A minimum thread protrusion 122(see FIG. 1A) dimensional requirement, (U_(min)), may also be verifiedby subtracting the actual nut thickness from measurement 266(P_(actual)), so that U_(min) will be satisfied if:U _(min) ≦P _(actual)−(actual nut thickness)  (1).By placing the nut 104 on the tool 260 over indicator end 220 of innerplug 212 and resting on gage surface 210, one could actually have thetool 260 “perform” this subtraction for the operator by simply readingthe protrusion from the index marking 262 visible at the top surface 113of nut 104 and checking that the protrusion is greater than or equal toU_(min).

As may be understood by one of ordinary skill in the art, any offastening system installation tools 200, 250, 260, and 270 may have atransducer and instrumentation attached and functionally connected tothe tool so as to display information given by the indicators—such asshoulders 224-228, color bands 252-258, and index markings 262. It maybe a routine matter, for example, to program or configureinstrumentation to make calculations such as equation (1) and displaythe results in any useful format. An example configuration of atransducer and display instrumentation attached to a fastening systeminstallation tool 280 is illustrated in FIG. 6A.

Referring now to FIG. 5, a fastening system installation tool 270 isillustrated in accordance with another embodiment. Fastening systeminstallation tool 270 may be similar in form and function to fasteningsystem installation tools 200, 250, and 260 and may include an outerhousing or sleeve 202, with a gage surface 210 and a base surface 208,which may be seated on a structure—such as structure 120 as shown inFIG. 5.

Tool 270 may also include an inner plug 212, with a sensing end 214, andan axial bore 216 so that sensing end 214 may reference the shanksection of a bolt—such as shank section 107 of bolt 102—as describedabove and as shown in FIG. 5. Inner plug 212 may include a dome 271having an axial opening 273 that guides axial translation of a plunger272. Inner plug 212 may include indicators such as threads-in-bearingshoulder 224 and shanking shoulder 225, which may be read, as describedabove, in conjunction with gage surface 210 or in conjunction withwashers—such as a washer 106—stacked on gage surface 210 to verify, forexample, both no threads-in-bearing and no shanking qualitativerequirements. As shown in FIG. 5, shoulder 225 may be provided on only aportion of the circumference of dome 271 so as not to preclude viewingof, in conjunction with shoulder 224, plunger index markings 276 onplunger 272. It may be easily understood that additional shoulders—suchas shoulders 226 and 228 of tool 200—may be added to tool 270 on onlyportions of the circumference of dome 271 so as not to preclude viewingof plunger index markings 276 in conjunction with shoulder 224. It mayalso be easily understood that tool 270 may be configured without anyadditional shoulders—such as shoulder 225—and may be provided only witha single shoulder such as shoulder 224.

Plunger 272 may have a sensing end 274 which may be designed toreference an end of a bolt—such as end 124 of bolt 102. Plunger 272 maybe made to have an interference fit or a sliding fit within axialopening 273 of inner plug 212. Axial bore 216 of inner plug 212 may alsobe adapted for a sliding or interference fit with a wide portion ofplunger 272 located near sensing end 274 of plunger 272 for guidingaxial translation of plunger 272 relative to inner plug 212. Plunger 272may include an indicator such as plunger index markings 276 which may beread in conjunction with shanking shoulder 225 to provide a measurement278, which may be, for example, a maximum pin protrusion measurement.Thus, plunger 272 may also, as described above, provide installationinformation, according to dimensional and qualitative requirements of afastening system installation specification, about components of thefastening system being installed using tool 270.

A minimum thread protrusion 122 (see FIG. 1A) dimensional requirement,(U_(min)), may also be verified using tool 270 according to thefollowing equations. Equation (2), which is similar to equation (1)above, uses P_(actual) to represent the actual pin protrusion that wouldbe measured for an actual washer stack to be installed with thefastening system.U=P _(actual)−(actual nut thickness)  (2)Thus, U represents the actual thread protrusion, for example, for agiven bolt 102 installed to a particular location in a structure 120using a given stack of washers 106 and a given nut 104. Therefore, tomeet U_(min) requires that U≧U_(min).

As shown in FIG. 5, tool 270 may be used to make certain measurementswithout the actual washer stack or actual nut. Pin protrusionmeasurement 278 may be made, as shown in FIG. 5, in conjunction withshanking shoulder 225 so that measurement 278 may give the amount ofthread length 108 of bolt 102 above thread transition zone 105.(Hypothetically, for example, pin protrusion measurement 278 could alsobe made in conjunction with threads-in-bearing shoulder 224 so thatmeasurement 278 would give the actual thread length 108 of bolt102—because inner plug 212 references the shank section 107 whileplunger 272 references the end 124 of bolt 102). Returning to FIG. 5,pin protrusion measurement 278 may, thus, correspond to the pinprotrusion that would be measured for an ideal washer stack of minimumthickness to prevent shanking, given the actual bolt 102. The thicknessof such an ideal minimum washer stack is shown in FIG. 5 as minimumwasher stack thickness 279 required to prevent shanking of bolt 102.

Equation (3), below uses P_(ideal), corresponding to measurement 278shown in FIG. 5, to represent the pin protrusion above the bearingsurface of the top washer of an ideal minimum washer stack for the givenbolt. (This roughly corresponds to maximum pin protrusion 110 dimensionshown in FIG. 1A.) Equation (3) uses A_(min) to represent the minimumwasher stack thickness 279 required to prevent shanking. Equation (3)relates the measurements shown in FIG. 5 (P_(ideal), A_(min)) to theactual pin protrusion (P_(actual)) and actual washer stack thickness.P _(actual) =P _(ideal)−(actual washer stack thickness−A _(min))  (3)Substituting equation (3) into equation (2) yields:U=P _(ideal)−(actual washer stack thickness−A _(min))−(actual nutthickness)  (4).

It should be noted that the minimum washer stack thickness 279measurement is the minimum washer stack required to prevent shanking,but the actual washer stack thickness may be bumped up to an actualwasher stack thickness exceeding the minimum washer stack thickness 279(A_(min)) because the washers only come in set increments, typically0.016 inches. Therefore, calculation of U without knowing the actualwasher stack thickness requires that the U value exceed U_(min) by onewasher thickness increment. Alternatively, or if the above process failsto yield U≧U_(min) by one washer thickness increment, the actual washersmay be incorporated on the tool 270, for example, by stacking them ongage surface 210, to make the pin protrusion measurement 278, whichwould effectively perform the subtraction of equation (3) or,equivalently the first two subtractions of equation (4) above. In otherwords, pin protrusion measurement 278 could be made in conjunction withthe top of a washer stack stacked on top of gage surface 210 so thatmeasurement 278 would give the actual pin protrusion (P_(actual) ratherthan P_(ideal)) above the bearing surface of the top washer of theactual washer stack to be installed (see equation (2)). Similarly onecould calculate the U value using the maximum nut height to see ifU_(min) is met. Alternatively, or if the maximum nut height causesU_(min) not to be met, the actual washers and nut may be incorporated onthe tool 270, for example, by stacking them on gage surface 210, to makethe pin protrusion measurement.

As described above, by placing the washers 106, or nut 104, or both, onthe tool 270 over inner plug 212, or plunger 272, or both, and stackedon gage surface 210, one could actually have the tool 270 “perform” someor all of the subtractions in the above equations for the operator bysimply reading from the plunger index markings 276 visible at the topsurface 111 of washer 106, for example, or the top surface 113 of nut104.

As noted above, fastening system installation tools 270 may have atransducer and instrumentation attached and functionally connected tothe tool 270 so as to display information given by the indicators—suchas shoulder 224 and index markings 276. Such instrumentation may beprogrammed or configured to make calculations such as equation (2) anddisplay the results in any useful format.

Referring now to FIGS. 6A and 6B, FIG. 6A shows a fastening systeminstallation tool 280 in accordance with another embodiment. Fasteningsystem installation tool 280 may be similar in form and function tofastening system installation tools 200, 250, 260, and 270 and mayinclude an outer housing or sleeve 202, with a gage surface 210 and abase surface 208, which may be seated on a structure—such as structure120 as shown in FIG. 6A.

Tool 280 may include an inner plug 212, with a sensing end 214, whichmay reference an end of a bolt—such as end 124 of bolt 102- or a shanksection of a bolt—such as shank section 107 of bolt 102—as shown in theexemplary embodiment illustrated in FIG. 6A. A transducer 282 may beattached, for example, to inner plug 212, and a transducer probe 284 maybe connected to outer housing 202, or may reference gage surface 210, sothat transducer 282 may measure, for example, relative displacement—suchas axial displacement 213 (shown in FIG. 2C)—between inner plug 212 andouter housing 202. Other configurations of connecting a transducerbetween inner plug 212 and outer housing 202 may be easily conceived,for example, attaching a transducer to outer housing 202 and connectingthe transducer probe to inner plug 212, or allowing a transducer probe284 to directly reference the end 124 of bolt 102. A transducer ortransducers may also be connected in various ways to the outer housing210, inner plug 212, and plunger 272 of tool 270, shown in FIG. 5, forproviding measurements corresponding, for example, to shoulders 224 and225, and plunger index markings 276 shown in FIG. 5. Also, for example,the transducer may be attached or connected to be removable andreplaceable for greater flexibility in the use of the tool—such as tool280.

Transducer 282 may incorporate a display 286, as shown in FIG. 6A, forexample, or may be provided with a separate display—such as hand-heldelectronic instrumentation with display—with a wiring harness connectingthe instrumentation and display to the transducer 282. The measurementsand display provided by instrumentation—such as transducer 282 anddisplay 286—may be used in the same manner as measurements and displayprovided by any of the indicators described above—such as shoulders 224,225, 226, and 228, color bands 252, 254, 256, and 258, index markings262, and plunger index markings 276—and may be used according to themethods described above. In an alternative embodiment, signal output oftransducer 282 may be connected to provide output to a controller of anautomatic fastening machine so that tool 280 may be incorporated as partof an automated fastening machine, for example, by mounting tool 280 toa robot arm subassembly of the automated fastening machine and providingtransducer 282 signals through a wring harness of the automatedfastening machine.

FIG. 6B illustrates an exemplary installation guide 290, in accordancewith an embodiment of the present invention, in the form of a tableshowing different alternative configurations for exemplary installationguide 290. The table of FIG. 6B shows an exemplary correspondence of atransducer 282 readout—in column 292—of fastening system installationtool 280 with exemplary installation guide 290 washer stackprescriptions—in columns 294 and 296—for stacking washers to achieve,for example, a fastening system installation in compliance with a noshanking qualitative requirement of a fastening system installationspecification.

For the exemplary installation guide 290 illustrated by the table ofFIG. 6B, the transducer 282 “plunger depth” of installation tool280—values of which are shown in column 292—may indicate, for example,relative displacement—such as axial displacement 213 (shown in FIG.2C)—between inner plug 212 and outer housing 202 so that the plungerdepth may be zero when base surface 208 and the surface of sensing end214 are co-planar. The “plunger depth” of transducer 282 thus does notinclude an amount of depth needed for a washer stack to cover up thethread transition zone 105 of bolt 102. For purposes of illustration,the depth of thread transition zone 105 is taken to be 0.016 inch in theexample used to illustrate the embodiment shown in FIGS. 6A and 6B. Thereadout in columns 294 and 296 may include an allowance for the depth ofthe thread transition zone 105. Thus, when the transducer 282 plungerdepth falls within one of the ranges shown in column 292, the prescribedwasher stack minimum height shown in the same row of column 294 or theprescribed washer stack description shown in the same row of column 296will be sufficient to cover the top of thread transition zone 105, forthe exemplary fastening system having a thread transition zone 105 of0.016 inch used in the illustration of FIGS. 6A and 6B.

For example, base surface 208 of tool 280 may be seated on structure 120and sensing end 214 of inner plug 212 may reference shank section 107 ofbolt 102 in accordance with the methods described above. Transducer 282may provide a measurement, for example, of axial displacement 213, forexample, of 0.034 inch, which may fall within the range indicated byentry 293 of column 292 in exemplary installation guide 290. Entry 293may correspond, for example, to entry 295 in column 294, which mayindicate that a washer stack with a minimum thickness of 0.064 inch isneeded for the installation being performed in order to meet a noshanking qualitative requirement. Exemplary installation guide 290 maybe specific to a fastening system, for example, that provides washers ineither of 16 mil (0.016 inch) and 32 mil (0.032 inch) optionalthicknesses so that entry 295 may indicate that the minimum thicknesswasher stack to meet no shanking is 0.064 inch. Thus, for a measurementin the range of 0.033 inch to 0.048 inch, display 286 may be configuredto display 0.064 in conformance with exemplary installation guide 290.Alternative types of display may be used. For example, for a measurementin the range of 0.033 inch to 0.048 inch, display 286 may be configuredto display “two 32 mil washers”—as indicated by entry 297 in column296—in conformance with exemplary installation guide 290.

It should be understood that an installation guide—such as exemplaryinstallation guide 290—can be used with any of the types of indicatorsdescribed above—such as shoulders 224, 225, 226, and 228, color bands252, 254, 256, and 258, index markings 262, and plunger index markings276—and can be used for predicting conforming installations for nuts andbolts as well as for washer stacks as illustrated by FIGS. 6A and 6B. Aninstallation guide—such as exemplary installation guide 290—can be useddirectly with a non-automated tool—such as tool 200 shown in FIGS. 2A,2B, and 2C —or may be programmed into a digital or automatedreadout—such as display 286—as shown by FIGS. 6A and 6B.

It should be understood, of course, that the foregoing relates topreferred embodiments of the invention and that modifications may bemade without departing from the spirit and scope of the invention as setforth in the following claims.

1. A fastening system installation tool for installation of a fasteningsystem to a structure, said tool comprising: an outer housing having aninterior hollow, a gage surface, and a base surface, said base surfacehaving a contact area that contacts the surface of the structure; aninner plug disposed within said interior hollow and that translatesaxially within said interior hollow, wherein: said inner plug has asensing end that contacts the fastening system; said inner plug has anindicator end dimensioned to accept washers and nuts of the fasteningsystem stacked on said gage surface; and said inner plug has anindicator at said indicator end that wherein said indicator of saidinner plug includes a shoulder, a position of said shoulder correlatingto a dimensional requirement which indicates whether a fastening systemcomponent conforms to a fastening system installation specification. 2.The fastening system installation tool of claim 1, wherein saidindicator provides installation information, according to a qualitativerequirement, about components of the fastening system being installedusing said tool.
 3. The fastening system installation tool of claim 1,wherein said indicator provides installation information, according to adimensional requirement of a fastening system installationspecification, about components of the fastening system being installedusing said tool.
 4. The fastening system installation tool of claim 1,wherein said sensing end of said inner plug has an axial bore, saidaxial bore having a diameter greater than the thread diameter of a boltof the fastening system but less than the shank diameter of a bolt ofthe fastening system.
 5. The fastening system installation tool of claim1, wherein said indicator of said inner plug includes a color band, athickness of said color band correlating to a dimensional requirement ofthe fastening system installation specification.
 6. The fastening systeminstallation tool of claim 1, wherein said indicator of said inner plugincludes a plurality of color bands and each of said color bandscorresponds to an available washer thickness of the fastening system. 7.The fastening system installation tool of claim 1, wherein saidindicator end of said inner plug includes a plurality of color bands, athickness of each said color band correlating to a distinct dimensionalrequirement of the fastening system installation specification. 8.(canceled)
 9. The fastening system installation tool of claim 1, whereinsaid indicator of said inner plug includes an index marking, a positionof said index marking correlating to a dimensional requirement of thefastening system installation specification.
 10. The fastening systeminstallation tool of claim 1, wherein said indicator of said inner plugprovides installation information about a washer stacked on said gagesurface.
 11. The fastening system installation tool of claim 1, whereinsaid indicator of said inner plug provides installation informationabout a nut stacked on said gage surface.
 12. The fastening systeminstallation tool of claim 1, wherein said inner plug references an endof a bolt of the fastening system.
 13. The fastening system installationtool of claim 1, further including: a plunger that references an end ofa bolt of the fastening system, said plunger having an indicator thatprovides installation information, according to a dimensionalrequirement of a fastening system installation specification, aboutcomponents of the fastening system being installed using said tool, andwherein: said sensing end of said inner plug has an axial bore, saidaxial bore having a diameter greater than the thread diameter of a boltof the fastening system but less than the shank diameter of a bolt ofthe fastening system; and said inner plug includes a dome, said domehaving an axial opening that guides an axial translation of saidplunger.
 14. A fastening system installation tool for installation of afastening system to a structure, said tool comprising: an outer housinghaving an interior hollow, a gage surface, and a base surface, said basesurface having a contact area that contacts the surface of thestructure; an inner plug disposed within said interior hollow and thattranslates axially within said interior hollow, wherein: said inner plughas a sensing end that contacts the fastening system; said inner plughas an indicator end dimensioned to accept washers and nuts of thefastening system stacked on said gage surface; and said inner plug hasan indicator on said indicator end wherein said indicator of said innerplug includes a shoulder, a position of said shoulder correlating to adimension requirement which indicates whether a fastening systemcomponent selection allows conformance to a qualitative requirement of afastening system installation specification.
 15. The fastening systeminstallation tool of claim 14, wherein: said fastening system componentselection is a bolt selection comprising a selected bolt; said sensingend of said inner plug references the end of the selected bolt of thefastening system; and said indicator of said inner plug is readable inconjunction with said gage surface to indicate whether the boltselection allows conformance to the fastening system installationspecification.
 16. The fastening system installation tool of claim 14,wherein: said fastening system component selection is a washer selectioncomprising a selected washer; said sensing end of said inner plugreferences the shank section of a bolt of the fastening system; and saidindicator of said inner plug is readable in conjunction with theselected washer stacked on said gage surface to indicate whether thewasher selection allows conformance to the fastening system installationspecification.
 17. The fastening system installation tool of claim 14,wherein: said fastening system component selection is a nut selectioncomprising a selected nut; said sensing end of said inner plugreferences the shank section of a bolt of the fastening system; and saidindicator of said inner plug is readable in conjunction with theselected nut stacked on said gage surface to indicate whether the nutselection allows conformance to the fastening system installationspecification.
 18. The fastening system installation tool of claim 14,wherein said outer housing has a base plate with a contact area that isa flat annular surface.
 19. The fastening system installation tool ofclaim 14, wherein said sensing end of said inner plug has an axial bore,and said axial bore is threaded to fit the threads of a bolt of thefastening system.
 20. (canceled)
 21. The fastening system installationtool of claim 14, wherein said indicator of said inner plug includes afirst shoulder and a second shoulder, a distance between said firstshoulder and said second shoulder correlating to a dimension requirementof the fastening system installation specification.
 22. A system forinstallation of a fastening system to a structure, said systemcomprising: a fastening system installation specification includingdimensional requirements for components of a fastening system; and atool including: an outer housing having an interior hollow, a gagesurface, and a base surface; said base surface having a contact areathat contacts the surface of the structure; an inner plug disposedwithin said interior hollow and that translates axially within saidinterior hollow, wherein: said inner plug has a sensing end thatcontacts and references the end of a bolt of the fastening system andreferences the shank section of a bolt of the fastening system, whereinsaid sensing end of said inner plug references the end of a bolt of thefastening system and said indicator end of said inner plug has anindicator that is readable in conjunction with said gage surface toindicate whether the bolt satisfies a minimum pin protrusion dimensionalrequirement of said fastening system installation specification; saidinner plug has an indicator end dimensioned to accept washers and nutsof the fastening system stacked on said gage surface; and said innerplug has an indicator on said indicator end that provides installationinformation according to said fastening system installationspecification about components of the fastening system being installedusing the tool.
 23. (canceled)
 24. The system of claim 22, wherein saidsensing end of said inner plug references the end of a bolt of thefastening system and said indicator end of said inner plug has anindicator that is readable in conjunction with said gage surface toindicate whether the bolt satisfies a maximum pin protrusion dimensionalrequirement of said fastening system installation specification.
 25. Thesystem of claim 22, wherein said sensing end of said inner plugreferences the shank section of a bolt of the fastening system and saidindicator end of said inner plug has a threads-in-bearing indicator thatis readable in conjunction with said gage surface to indicate whetherthe bolt satisfies a no threads in bearing requirement of said fasteningsystem installation specification.
 26. The system of claim 22, whereinsaid sensing end of said inner plug references the shank section of abolt of the fastening system and said indicator end of said inner plughas a shanking indicator that is readable in conjunction with a washerstacked on said gage surface to indicate whether the washer satisfies ano shanking requirement of said fastening system installationspecification.
 27. The system of claim 22, wherein said sensing end ofsaid inner plug references the shank section of a bolt of the fasteningsystem and said indicator end of said inner plug has a thread boltprotrusion indicator that is readable in conjunction with a nut stackedon said gage surface to indicate whether the nut satisfies a minimumthread protrusion requirement of said fastening system installationspecification.
 28. An installation system for installing aerospacefastening systems to a structure, said installation system comprising:an installation guide in accordance with qualitative requirements forcomponents of a fastening system; and a tool including: an outer housinghaving an interior hollow, a gage surface, and a base surface, said basesurface having a flat contact area that contacts the surface of thestructure; an inner plug disposed within said interior hollow and thattranslates axially within said interior hollow, wherein: said inner plughas a sensing end with an axial bore that contacts the fastening system,and said sensing end references the shank section of a bolt of thefastening system; said inner plug has an indicator end; a transducerconnected between said outer housing and said inner plug, and thatmeasures a relative displacement between said inner plug and said outerhousing; and an electronic instrumentation connected to said transducerand that provides and displays installation information according tosaid installation guide about whether the bolt, washer, and nutcomponents of the fastening system being installed using the tool willconform to a fastening system installation specification.
 29. Theinstallation system of claim 28 wherein said installation guide includesa prescription for a washer stack corresponding to said relativedisplacement measured by said transducer.
 30. The installation system ofclaim 28 wherein said installation information includes a prescriptionaccording to said installation guide for a washer stack corresponding tosaid relative displacement measured by said transducer.
 31. Theinstallation system of claim 28 further comprising: a plunger thatreferences an end of a bolt of the fastening system, wherein: said innerplug includes a dome, said dome having an axial opening that guides anaxial translation of said plunger; and said transducer is connected tosaid plunger.
 32. A method for installing aerospace fastening systems toa structure, comprising the steps of: seating a base of an outer housingof a tool to a surface of the structure; referencing a shank section ofa bolt of the fastening system with an Inner plug of said tool; readinga threads-in-bearing indicator of said inner plug in conjunction with agage surface of said outer housing; replacing the bolt when saidthreads-in-bearing indicator is not above said gage surface; andinstalling the bolt when said threads-in-bearing indicator is above saidgage surface.
 33. The method of claim 32, wherein said replacing step isperformed due to not meeting a no threads in bearing requirement of afastening system installation specification.
 34. The method of claim 32,wherein said inner plug of said tool has a shanking indicator andfurther comprising steps of: stacking a first washer on said gagesurface to form a stack; reading a shanking indicator of said inner plugin conjunction with the top of the stack; adding an additional washer tothe stack when the top of the stack is below said shanking indicator;and adding a nut to the stack when the top of the stack is not belowsaid shanking indicator.
 35. The method of claim 34, wherein said addingan additional washer step is performed due to not meeting a no shankingrequirement of a fastening system installation specification.
 36. Themethod of claim 32, further comprising steps of: reading a thread boltprotrusion indicator of said inner plug in conjunction with a nutstacked on said gage surface; replacing the nut when the top of the nutis above said thread bolt protrusion indicator; and installing the nutwhen the top of the nut Is below said thread bolt protrusion indicator.37. The method of claim 32, further comprising steps of: reading athread bolt protrusion indicator of said inner plug in conjunction witha nut stacked on said gage surface; replacing the bolt when the top ofthe nut is above said thread bolt protrusion indicator; and installingthe nut when the top of the nut is below said thread bolt protrusionindicator.
 38. The method of claim 36, wherein said replacing step isperformed due to not meeting a complete nut engagement requirement of afastening system installation specification.
 39. The method of claim 37,wherein said replacing step is performed due to not meeting a completenut engagement requirement of a fastening system installationspecification.
 40. A method for installing aerospace fastening systemsto a structure, comprising the steps of: inserting a bolt of thefastening system in a hole of the structure; checking for a protrusionof a shank section of the bolt above a surface of the structure;replacing the bolt when the shank section does not protrude above thesurface of the structure; seating a base of an outer housing of a toolto a surface of the structure; referencing a shank section of a bolt ofthe fastening system with an inner plug of said tool; stacking a firstwasher on a gage surface of said tool to form a stack; reading ashanking indicator of said inner plug in conjunction with the top of thestack; and adding an additional washer to the stack when the top of thestack is below said shanking indicator.
 41. The method of claim 40,wherein said replacing step is performed due to not meeting a no threadsin bearing requirement of a fastening system installation specification.42. The method of claim 40, further comprising a step of: adding a nutto the stack when the top of the stack is not below said shankingindicator.
 43. The method of claim 40, wherein said adding an additionalwasher step is performed due to not meeting a no shanking requirement ofa fastening system installation specification.
 44. A method forinstalling an aerospace fastening system to a structure, comprising thesteps of: seating a base of an outer housing of a tool to a surface ofthe structure; referencing a shank section of a bolt of the fasteningsystem with an inner plug of said tool; reading an indicator of saidtool to determine a prescribed washer stack for the fastening system.45. The method of claim 44, wherein said step of reading an indicatorincludes reading an output display generated from a transducer connectedto said tool.
 46. The method of claim 44, further comprising a step of:installing a washer stack as prescribed from reading said indicator. 47.The method of claim 44, wherein said prescribed washer stack isprescribed according to an installation guide in accordance with afastening system installation specification.
 48. A method foreliminating trial and error in installing an aerospace fastening systemto a structure, comprising the steps of: querying at least one dimensionof the actual fastening system hardware using a fastening systeminstallation tool having an inner plug, with indicators, disposed toaxially translate within an outer housing; and determining an actualwasher stack to install on the fastening system so that said fasteningsystem installation conforms to a qualitative requirement.
 49. Themethod of claim 48 wherein said qualitative requirement is chosen fromthe group consisting of: (1) no “threads in bearing”; (2) no “shanking”;and (3) complete nut engagement.
 50. The method of claim 48 wherein saidquerying step includes measuring a thread length of an actual bolt ofthe fastening system.
 51. The method of claim 48 wherein: the actualfastening system hardware is applied to the structure; and said queryingstep includes measuring a protrusion through the structure of an actualbolt of the fastening system.
 52. The method of claim 48 wherein saidquerying step includes querying a washer of the fastening system. 53.The method of claim 48 wherein said querying step includes querying anut of the fastening system.
 54. An automated fastening machineincluding: an outer housing having an interior hollow, a gage surface,and a base surface, said base surface having a flat contact area; aninner plug disposed within said interior hollow and that translatesaxially within said interior hollow, wherein: said inner plug has asensing end with an axial bore, and said sensing end contacts afastening system and references the shank section of a bolt of thefastening system; and said inner plug has an indicator end; a transducerconnected between said outer housing and said inner plug, and thatmeasures a relative displacement between said inner plug and said outerhousing; and an electronic instrumentation connected to said transducer.55. The automated fastening machine of claim 54 wherein: said electronicinstrumentation is a controller that controls installation of thefastening system being installed by said automated fastening machine.56. The automated fastening machine of claim 54 wherein: said electronicinstrumentation uses a signal from said transducer to decide whether abolt, washer, and nut components of the fastening system being installedusing the automated fastening machine will conform to a fastening systeminstallation specification.